Trench type non-volatile memory having three storage locations in one memory cell

ABSTRACT

A non-volatile memory. The non-volatile memory comprises a substrate, a conductive layer, a charge storage layer, several first doped regions and several second doped regions. The substrate has a plurality of trenches formed therein. The conductive layer is located over the substrate, wherein the conductive layer fills in the trenches. The charge storage layer is located between the substrate and the conductive layer. The first doped regions are located in the substrate adjacent to both sides of the trenches respectively, wherein the first doped regions between the neighboring trenches are separated from each other. The second doped regions are located in a portion of the substrate under the bottoms of the trenches respectively.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a semiconductor device and a manufacturing method thereof. More particularly, the present invention relates to a non-volatile memory and a fabricating method thereof.

2. Description of Related Art

The electrically erasable programmable read only memory (EEPROM) possesses the ability to store, read and erase data for several times. Moreover, the EEPROM has the advantage that the stored data is not lost even after the system is power off. Therefore, the EEPROMs are widely used in the personal computers and electronic equipments.

Typical EEPROM is composed of a floating gate and a control gate, which are made of doped polysilicon. When the memory is programmed, the electrons injected into the floating gate uniformly distributes in the polysilicon floating gate layer. However, when there are defects in the tunnel oxide layer under the polysilicon floating gate layer, the leakage is easily produced in the device. Hence, the reliability of the device is decreased.

Currently, in order to solve the leakage problem of the EEPROM, a charge storage layer is used to substitute the polysilicon floating gate. The charge storage layer is made of silicon nitride. Usually, each side of the silicon nitride charge storage layer has a silicon oxide layer so as to form a stacked gate structure including a silicon oxide/silicon nitride/silicon oxide (ONO) complex dielectric layer.

In addition, another advantage obtained from replacing the polysilicon floating gate with the silicon nitride layer is that the electrons are only stored in a portion of the silicon nitride layer over the channel region adjacent to the source region or drain region while the device is programmed. Therefore, during the programming process, the voltages can be applied on the source region and the control gate respectively. Hence, the electrons are stored in a portion of the silicon nitride layer near the drain region with a form of Gaussian distribution. Alternatively, the voltages can be applied on the drain region and the control gate respectively. Hence, the electrons are stored in a portion of the silicon nitride layer near the source region with a form of Gaussian distribution. On the other words, there are two storage regions in a single silicon nitride layer. By properly applying the voltages on the control gate and on either the source region or the drain region, there can be four different storage states, which includes each of the storage regions having one group of electrons with a Gaussian distribution property, either one of the storage regions having one group of electrons with a Gaussian distribution property and none of the electrons stored in both storage regions, in a single silicon nitride layer. That is, a single flash memory cell can present four different storage states. Hence, instead of using the floating gate, the flash memory with a silicon nitride charge storage layer is considered a 2-bit-per-cell memory.

Conventionally, in order to increase the number of bits of a unit cell, a memory structure with a vertical memory cell is developed. This kind of memory cell is a 4-bit-per-cell flash memory. However, between two vertical memory cells, the phenomenon of electron punching through happens easily. Hence, the leakage in the memory structure is induced.

SUMMARY OF THE INVENTION

Accordingly, at least one objective of the present invention is to provide a non-volatile memory capable of increasing the number of bits of a unit cell.

At least another objective of the present invention is to provide a method for manufacturing a non-volatile memory with high density of storage regions.

At least the other objective of the present invention is to provide a method for manufacturing a 3-bit-per-cell non-volatile memory.

To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a non-volatile memory. The non-volatile memory comprises a substrate, a conductive layer, a charge storage layer, several first doped regions and several second doped regions. The substrate has a plurality of trenches formed therein. The conductive layer is located over the substrate, wherein the conductive layer fills in the trenches. The charge storage layer is located between the substrate and the conductive layer. The first doped regions are located in the substrate adjacent to both sides of the trenches respectively, wherein the first doped regions between the neighboring trenches are separated from each other. The second doped regions are located in a portion of the substrate under the bottoms of the trenches respectively.

In the present invention, the charge storage layer is made of silicon nitride. Also, the present invention further comprises a first dielectric layer located under the charge storage layer, wherein the first dielectric layer is made of silicon oxide. In addition, the present invention further comprises a second dielectric layer located above the charge storage layer, wherein the second dielectric layer is made of silicon oxide. Moreover, the conductive layer is made of doped polysilicon. Also, the non-volatile memory can be a multi-level cell.

The present invention also provides a method for manufacturing a non-volatile memory. The method comprises steps of providing a substrate. Thereafter, a plurality of first doped regions are formed in the substrate and then a plurality of trenches are formed in a portion of the first doped regions. A plurality of second doped regions are formed in a portion of the substrate under the bottoms of the trenches respectively. Then, a charge storage layer is formed conformal to a surface of the substrate and a conductive layer is formed over the substrate, wherein the conductive layer covers the charge storage layer and fills in the trenches.

According to the present invention, the method for forming the first doped regions, the trenches and the second doped regions comprises steps of forming a patterned mask layer on the substrate and then forming the first doped regions in the substrate exposed by the patterned mask layer. A spacer is formed on the sidewall of the patterned mask layer, wherein the spacer covers a portion of the first doped region. The trenches are formed in the substrate exposed by the patterned mask layer and the spacer. The second doped regions are formed under the bottoms of the trenches in the substrate exposed by the patterned mask layer and the spacer. The patterned mask layer and the spacer are removed. The method for forming first doped regions and the second doped regions in the aforementioned method includes an ion implantation process. In the aforementioned method, the patterned mask layer is made of silicon oxide and the spacer is made of silicon nitride or silicon oxide. The method for forming the spacer in the aforementioned method comprises steps of forming a dielectric layer over the substrate, wherein the dielectric layer covers the patterned mask layer and performing a dry etching process on the dielectric layer. In one embodiment, the method for forming the trenches and the second doped regions comprises steps of forming a patterned mask layer on the substrate to expose a portion of the first doped regions respectively and then forming the trenches in a portion of the substrate exposed by the patterned mask layer. The second doped regions are formed in the substrate under the bottoms of the trenches respectively. The patterned mask layer is removed. The method for forming the second doped regions in the aforementioned method includes an ion implantation process. The charge storage layer is made of silicon nitride. Furthermore, the method further comprises a step of forming a first dielectric layer between the charge storage layer and the substrate, wherein the first dielectric layer is made of silicon oxide. Moreover, the method further comprises a step of forming a second dielectric layer between the charge storage layer and the conductive layer, wherein the second dielectric layer is made of silicon oxide.

The memory of the present invention has the vertical memory structure and the horizontal memory structure and is a 3-bit-per-cell non-volatile memory. Therefore, the number of the bit storing in a unit cell is increased. According to the present invention, there are three storage regions in a single memory cell so that the storage density of the memory of the present invention is relatively high.

It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

FIG. 1 is a cross-sectional view showing a non-volatile memory according to one preferred embodiment of the present invention.

FIGS. 2A through 2D are cross-sectional views illustrating a method for manufacturing a non-volatile memory according to one preferred embodiment of the present invention.

FIGS. 3A through 3C are cross-sectional views illustrating a method for manufacturing a non-volatile memory according to one preferred embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a cross-sectional view showing a non-volatile memory according to one preferred embodiment of the present invention.

As shown in FIG. 1, the non-volatile memory of the present invention comprises a substrate 100, a conductive layer 102, a complex dielectric layer 104, several first doped regions 106 and several second doped regions 108. The substrate 100 has several trenches 110 and the substrate 100 can be, for example but not limited to, a silicon substrate.

The conductive layer 102 is located over the substrate 100 and fills in the trenches 110. The conductive layer 102 can be, for example but not limited to, made of doped polysilicon.

The complex dielectric layer 104 is located between the conductive layer 102 and the substrate 100. The complex layer 104 can be, for example but not limited to, composed of a bottom dielectric layer 104 a, a charge storage layer 104 b and a top dielectric layer 104 c, wherein the bottom dielectric layer 104 a and the top dielectric layer 104 c can be, for example but not limited to, made of silicon oxide and the charge storage layer can be, for example but not limited to, formed of silicon nitride.

The first doped regions 106 are located at both sides of each of the trenches 110 in the substrate 100 respectively, wherein the first doped regions 106 between the neighboring trenches 110 are separated from each other. Further, the conductive type of the first doped regions 106 can be, for example but not limited to, N type.

The second doped regions 108 are located in the substrate 100 under the bottom of the trenches 110 respectively. Additionally, the conductive type of the second doped regions 108 can be, for example but not limited to, N type.

The non-volatile memory of the present invention can be, for example but not limited to, a multi-level cell (MLC) used for storing multi charges according different programming levels. Taking the memory cell 112 in FIG. 1 as an example, a 2-bit storing process can be performed in a portion of the complex dielectric layer 104 located over the sidewall of the trench 110. Moreover, a 1-bit storing process can be performed in a portion of the complex dielectric layer 104 located between the trenches 110. Therefore, the non-volatile memory of the present invention is a 3-bit-per-cell non-volatile memory. By comparing with the conventional stacked flash memory, storage density of the non-volatile memory is relatively high.

FIGS. 2A through 2D are cross-sectional views illustrating a method for manufacturing a non-volatile memory according to one preferred embodiment of the present invention.

As shown in FIG. 2A, a substrate 200 is provided. A patterned mask layer 202 is formed on the substrate 200. The patterned mask layer 202 can be, for example but not limited to, made of silicon oxide. The method for forming the patterned mask layer 202 comprises steps of forming a mask material layer (not shown) on the substrate 200 by chemical vapor deposition (CVD), forming a patterned photoresist layer 204 on the mask material layer and then performing an etching process to pattern mask material layer by using the patterned photoresist layer 204 as a mask until the patterned mask layer 202 is formed.

As shown in FIG. 2B, the patterned photoresist layer 204 is removed. Then, a plurality of first doped regions 206 are formed in a portion of the substrate 200 exposed by the patterned mask layer 202. The first doped regions can be, for example but not limited to, N-type doped regions. The method for forming the first doped regions comprises a step of performing an ion implantation process for implanting phosphorous ions into the substrate 200 by using the patterned mask layer 202 as a mask.

Thereafter, a spacer 208 is formed on the sidewall of the patterned mask layer 202 over the substrate 200, wherein the spacer 208 covers a portion of the first doped regions 206. Moreover, the spacer 208 can be, for example but not limited to, made of silicon nitride or silicon oxide. The method for forming the spacer 208 comprises steps of forming a dielectric layer (not shown) over the substrate 200 by using the CVD and then performing a dry etching process on the dielectric layer until the spacer 208 is formed.

As shown in FIG. 2C, an etching process is performed to form several trenches 210 in the substrate 200 by using the patterned mask layer 202 and the spacer 208 as masks. The etching process can be, for example but not limited to, a dry etching process.

Moreover, a plurality of second doped regions 212 are formed in the substrate 200 under the bottom of the trenches 210 respectively. The second doped regions 212 can be, for example but not limited to, N-type doped regions. The method for forming the second doped regions 212 comprises a step of performing an ion implantation process for implanting phosphorous ions into the substrate 200 by using the patterned mask layer 202 and the spacer 208 as masks.

As shown in FIG. 2D, the patterned mask layer 202 and the spacer 208 are removed. The method for removing the patterned mask layer 202 and the spacer 208 can be, for example but not limited to, a dry etching process.

Then, a complex dielectric layer 214 is conformally formed over the substrate 200. The method for forming the complex dielectric layer 214 comprises steps of forming a bottom dielectric layer 214 a, a charge storage layer 214 b and a top dielectric layer 214 c over the substrate 200 sequentially. The bottom dielectric layer 214 a can be, for example but not limited to, formed from silicon oxide by using thermal oxidation or CVD. The charge storage layer 214 b can be, for example but not limited to, formed from silicon nitride by using CVD. Also, the top dielectric layer 214 c can be, for example but not limited to, formed from silicon oxide by using CVD.

Thereafter, a conductive layer 216 is formed over the substrate 200. The conductive layer 216 covers the complex dielectric layer 214 and fills in the trenches 210. The conductive layer 216 can be, for example but not limited to, formed from doped polysilicon by using polysilicon CVD with in-situ dopping.

The memory formed by applying the aforementioned method has the vertical memory structure and the horizontal memory structure. That is, the memory is a 3-bit-per-cell non-volatile memory with relatively high storage density.

FIGS. 3A through 3C are cross-sectional views illustrating a method for manufacturing a non-volatile memory according to one preferred embodiment of the present invention.

As shown in FIG. 3A, a substrate 300 is provided. A patterned mask layer 302 is formed on the substrate 300. The patterned mask layer 302 can be, for example but not limited to, a photoresist layer. The method for forming the patterned mask layer 302 comprises steps of forming a photoresist layer (not shown) over the substrate 300 and then performing an exposure and development process on the photoresist layer.

Then, several first doped regions 306 are formed in a portion of the substrate 300 exposed by the patterned mask layer 302. The first doped regions 306 can be, for example but not limited to, N-type doped regions. The method for forming the first doped regions 306 comprises a step of performing an ion implantation process for implanting phosphorous ions into the substrate 300 by using the patterned mask layer 302 as a mask.

As shown in FIG. 3B, the patterned mask layer 302 is removed. A patterned mask layer 308 is formed over the substrate 300 to expose a portion of the first doped regions 306. The patterned mask layer 308 can be, for example but not limited to, a photoresist layer. The method for forming the patterned mask layer 308 comprises steps of forming a photoresist layer (not shown) over the substrate 300 and then performing an exposure and development process on the photoresist layer.

By using the patterned mask layer 308 as mask, an etching process is performed on the substrate 300 to form several trenches 310 in the substrate 300. The etching process can be, for example but not limited to, a dry etching process.

Then, several second doped regions 312 are formed in a portion of the substrate 300 under the bottom of the trenches 310 respectively. The second doped regions 312 can be, for example but not limited to, N-type doped regions. The method for forming the second doped regions 312 comprises a step of performing an ion implantation process for implanting phosphorous ions into the substrate 300 by using the patterned mask layer 308 as mask.

As shown in FIG. 3C, the patterned mask layer 308 is removed. The method for removing the patterned mask layer 308 includes a dry etching process.

Then, a complex dielectric layer 314 is conformally formed over the substrate 300. The method for forming the complex dielectric layer 314 comprises steps of forming a bottom dielectric layer 314 a, a charge storage layer 314 b and a top dielectric layer 314 c over the substrate 300 sequentially. The bottom dielectric layer 314 a can be, for example but not limited to, formed from silicon oxide by using thermal oxidation or CVD. The charge storage layer 314 b can be, for example but not limited to, formed from silicon nitride by using CVD. Also, the top dielectric layer 314 c can be, for example but not limited to, formed from silicon oxide by using CVD.

Thereafter, a conductive layer 316 is formed over the substrate 300. The conductive layer 316 covers the complex dielectric layer 314 and fills in the trenches 310. The conductive layer 316 can be, for example but not limited to, formed from doped polysilicon by using polysilicon CVD with in-situ dopping.

The memory formed by applying the aforementioned method has the vertical memory structure and the horizontal memory structure. That is, the memory is a 3-bit-per-cell non-volatile memory with relatively high storage density.

Altogether, the present invention has the following advantages:

-   (1) The non-volatile memory of the present invention has the     vertical memory structure and the horizontal memory structure and is     a 3-bit-per-cell non-volatile memory. Therefore, the number of the     bit storing in a unit cell is increased. -   (2) According to the present invention, there are three storage     regions in a single memory cell so that the storage density of the     memory of the present invention is relatively high.

It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing descriptions, it is intended that the present invention covers modifications and variations of this invention if they fall within the scope of the following claims and their equivalents. 

What is claimed is:
 1. A non-volatile memory, comprising: a substrate having a plurality of trenches formed therein; a conductive layer located over the substrate, wherein the conductive layer fills in the trenches; a plurality of first doped regions located in the substrate adjacent to both sides of the trenches respectively, wherein the first doped regions between the neighboring trenches are separated from each other; a plurality of second doped regions located in a portion of the substrate under the bottoms of the trenches respectively, and a charge storage layer located between the substrate and the conductive layer, extending from the bottoms of the trenches, the sidewalls of the trenches, and a surface of the first doped regions to a surface of the substrate separating and directly connecting two adjacent first doped regions of two different cells, so as to form three storage locations in one memory cell.
 2. The non-volatile memory of claim 1, wherein the charge storage layer is made of silicon nitride.
 3. The non-volatile memory of claim 1 further comprising a first dielectric layer located under the charge storage layer.
 4. The non-volatile memory of claim 3, wherein the first dielectric layer is made of silicon oxide.
 5. The non-volatile memory of claim 1 further comprising a second dielectric layer located above the charge storage layer.
 6. The non-volatile memory of claim 5, wherein the second dielectric layer is made of silicon oxide.
 7. The non-volatile memory of claim 1, wherein the conductive layer is made of doped polysilicon.
 8. The non-volatile memory of claim 1, wherein the non-volatile memory is a multi-level cell.
 9. A non-volatile memory, comprising: a substrate having a plurality of trenches formed therein; a plurality of first doped regions located in the substrate adjacent to both sides of the trenches respectively, wherein the first doped regions between the neighboring trenches are separated from each other; a plurality of second doped regions located in a portion of the substrate under the bottoms of the trenches respectively; a charge storage stacked layer made of dielectric materials located over and contacting the bottoms of the trenches, the sidewalls of the trenches, a first surface of the first doped regions and a second surface of the substrate separating and directly connecting two adjacent first doped regions of two different cells; and a conductive layer directly contacting an entire of the charge storage stacked layer located over and contacting the bottoms of the trenches, the sidewalls of the trenches, the first surface of the first doped regions and the second surface of the substrate separating and directly connecting two adjacent first doped regions of two different cells, so as to form three storage locations in one memory cell.
 10. The non-volatile memory of claim 9, wherein each trench is only filled with the conductive layer and the charge storage stacked layer.
 11. The non-volatile memory of claim 9, wherein the second surface of the substrate is coplanar to the first surfaces of the first doped regions.
 12. The non-volatile memory of claim 9, wherein the charge storage stacked layer comprises a silicon nitride layer.
 13. The non-volatile memory of claim 12, wherein the charge storage stacked layer further comprises a silicon oxide layer located under or above the silicon nitride layer.
 14. The non-volatile memory of claim 12, wherein the charge storage stacked layer further comprises a silicon oxide layer under and above the silicon nitride layer.
 15. The non-volatile memory of claim 9, wherein a first portion of the conductive layer located over each first doped regions is located between a second portion of the conductive layer located over an adjacent second doped regions and a third portion of the conductive layer located over an adjacent second surface.
 16. The non-volatile memory of claim 9, wherein the non-volatile memory is a multi-level cell. 